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Surface characterization of cast Ti-6Al-4V in hydrofluoric-nitric pickling solutions

Elsevier B.V.
Publication Date
DOI: 10.1016/s0257-8972(03)00747-3
  • Alpha-Case
  • Pickling Solutions
  • Polarization
  • Passive Film
  • Non-Stoichiometric
  • Chemistry


Abstract Hydrofluoric acid offers a fast etching rate for removing 200 μm-thick alpha-cases from the surfaces of cast Ti-6Al-4V. The acid picks up hydrogen gas into substrate of the cast, which can be limited by introducing an oxidizing acid. This study proposes the optimal ratios of hydrofluoric/nitric acid as the pickling solutions. The cast Ti-6Al-4V in these solutions is monitored with chemical etching and electrochemical polarization. The mechanisms of etching procedures are initiated by generating oxygen vacancies that lead to several products from a series of quasi-chemical steps. The final product of the reactions may deduce as the form of H 2TiF 6 that is peeled out by the evolution of produced gases. Polarized curves are performed to illustrate passive behaviors of the alpha-case removed Ti-6Al-4V. The amounts of charge transference increase with increasing hydrofluoric acid concentrations. The newly formed passive film was estimated to be 20 nm in thickness with non-stoichiometric arrangements in the 4% HF electrolyte.

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